Electronic dimmable windows are becoming increasingly common in a wide variety of industries, such as on vehicles and in building construction. They provide the ability to change color or degree of opacity of the window, and thereby adjust light transmission through the window, simply by switching a controlling electrical power signal. Electronic dimmable windows are typically multi-layer assemblies. Outer layers of the electronic dimmable window typically are electrodes that are optically clear (i.e., substantially transparent to light in wavelengths of the visible spectrum or at other desired wavelengths, albeit in some instances bearing a limited tint or color). At least one electrochromic layer is sandwiched between the outer electrode layers. The electrochromic layer is able to change color or opacity in response to changes in an applied electric field or current to create visual effects. The electrochromic layer is often an organic polymer film or an inorganic thin film of electrochromic material. When an electric field is applied to the outer electrode layers, ions in an electrolyte typically move to the electrochromic layer causing the electrochromic material to change color states. Reversing the electric field moves ions away from the electrochromic layer, restoring the device to its previous state. Electrolytes may be in the form of a liquid or gel.
In the aerospace industry, electronic dimmable windows have started to replace pull down shades of windows in passenger cabins of aircraft, such as commercial airliners. Aircraft window systems generally include a window pane formed with a window outer pane and window inner pane arranged in a stacked configuration adjacent to each other. An electronic dimmable window is positioned adjacent the window inner pane. A dust cover is positioned adjacent the electronic dimmable window such that the electronic dimmable window is between the dust cover and the window pane. Thus, the window pane forms an outer surface when coupled with an aircraft fuselage and the dust cover forms an inner surface within the passenger cabin. Additional components may be provided in the window system.
Cracks may form in electronic dimmable windows in aircraft window systems during in-flight operation, particularly in window systems located proximate the wings of an aircraft, and more particularly in window systems located proximate the wings of an aircraft having wings with deflected wing tips. Such localized cracks make the electronic dimmable window less effective, but do not otherwise affect the window systems.
FIG. 1 shows a partial front view of a typical aircraft 10 having wings 12 with a deflected wing tip 14 deflected in an upward direction from the plane 16 of the wings 12. In such aircraft, direct sunlight 18 may directly impinge upon the aircraft 10, including the aircraft's window systems and thus the electronic dimmable windows in such window systems; and indirect sunlight 20, including multiple solar rays 22, may be reflected from the wing tips 14 and combined with the direct sunlight 18 to cause substantial increases in solar flux intensity directed through the window systems and electronic dimmable windows.
FIG. 2 is an exploded view of a typical window system 24 illustrating light rays passing through the window system. Such window systems 24 generally comprise a window pane 26, an electronic dimmable window 28 and dust cover 30, with the electronic dimmable window 28 positioned adjacent and between the window pane 26 and the dust cover 30. Direct sunlight 18 generally forms uniform direct rays 32 that pass through the window panes 26. The multiple solar rays 22 of indirect sunlight 20 generally form one or more localized spikes of high solar flux intensity 34 where the direct sunlight 18 and indirect sunlight 20 are combined, which can fluctuate in location and intensity. When the electronic dimmable window 28 is in a dark mode (i.e., such that it blocks out sunlight), the one or more localized spikes of high solar flux intensity 34 penetrate onto the electronic dimmable window 28 in a local area 38, resulting in much higher energy absorption in the local area 38. Higher energy absorption causes a spike in the temperature of the electronic dimmable window 28 in the local area 38 but not in other areas, i.e., there is a non-uniform temperature excursion in the electronic dimmable window 28, and causes cyclic high local thermal induced stresses in the local area 38 of the electronic dimmable window as the localized spikes of high solar flux intensity 34 fluctuate, ultimately initiating a crack 36 in the electronic dimmable window 28 at the local area 38. It would therefore be beneficial to minimize or eliminate spikes of high solar flux intensity 34 to avoid high local thermal induced stresses and the resulting cracks to improve the usefulness and reliability of electronic dimmable windows.